Automobile bodies are formed by joining a plurality of tabular panel materials which are workpieces, and when spot welding is performed, there is a need to position and clamp various panel materials constituting the automobile bodies. Therefore, a plurality of positioning and clamping apparatuses are attached to welding stages allocated on automobile production lines in order to position and fix the panel materials. Positioning and clamping apparatuses are mounted to tips of robot arms when the workpieces are clamped and carried out by industrial robots. Positioning and clamping apparatuses are mounted to carrying-out carriages when the workpieces are positioned and clamped by the positioning and clamping apparatuses.
In any case, a conventional positioning and clamping apparatus is configured to fit a locating pin in a positioning hole formed in a panel material to position the panel material, and clamp the panel material by a clamp arm built into a slit formed in the locating pin. It is necessary to detect whether or not the panel material is fitted in the locating pin and positioned at a predetermined position when the panel material is clamped, and the positioning and clamping apparatus including such detecting means, for example, is disclosed in Patent Document 1 (Japanese Patent Application Laid-Open Publication No. 2003-260626).